Display device and operating method thereof

ABSTRACT

A display device may include a pixel, an emission control driver, and a timing controller. The emission control driver may supply an emission control signal set for controlling emission periods of the pixel. The timing controller may receive a received bit stream that includes a first bit set and a second bit set, may determine a first duty ratio of the emission control signal set using bits of the first bit set without using any bit of the second bit set. The first bit set may include at least two bits. The second bit set may include at least one bit. The emission control signal set may control the pixel to operate according to the first duty ratio for each frame of a first frame group.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of U.S. patentapplication Ser. No. 16/046,788, filed on Jul. 26, 2018, which claimspriority to Korean Patent Application No. 10-2017-0135135 filed on Oct.18, 2017 in the Korean Intellectual Property Office; the entiredisclosure of the Korean Patent Application is incorporated by referenceherein.

BACKGROUND 1. Field

The technical field relates to a display device and an operating methodof the display device.

2. Description of the Related Art

A display device, such as an organic light emitting display device, maydisplay images using organic light emitting diodes that generate lightby combination of electrons and holes. An organic light emitting displaydevice may have a high response speed and may operate with low powerconsumption.

An organic light emitting display device may display a target image byproviding a data voltage in each pixel for the corresponding organiclight emitting diode to emit light according to the data voltage.

SUMMARY

Embodiments may be related to a display device capable of expressing adimming level similar to a target dimming level with minimum switchingpower consumption of a dimming controller. Embodiments may be related toa driving method (i.e., operating method) of the display device.

Embodiments may be related to a display device having a satisfactorynumber of expressible dimming levels and including a low-resolutiondisplay panel. Embodiments may be related to a driving method of thedisplay device.

According to an embodiment, a display device may include the followingelements: a pixel unit including a plurality of pixels; an emissioncontrol driver configured to supply an emission control signal fordetermining an emission period of the plurality of pixels; and a timingcontroller configured to determine a duty ratio of the emission controlsignal, using a duty ratio bit stream configured with m bits, whereinthe timing controller determines the duty ratio bit streamincluding m−kmost significant bits (MSBs) and k least significant bits (LSBs) havinga fixed value, during n frames, wherein the k is a natural number of 1or more, and the n and m are natural numbers of 2 or more.

The n may be 2^(k).

Frames of a first group among the n frames may be emission-controlled tocorrespond to the duty ratio bit stream which is a first duty ratio bitstream, frames of a second group among the n frames may beemission-controlled to correspond to the duty ratio bit stream which isa second duty ratio bit stream, and the first duty ratio bit stream andthe second duty ratio bit stream are different.

The second duty ratio bit stream may have a value obtained by adding 2^(k) to a value of the first duty ratio bit stream.

The frames of the first group and the frames of the second group may betime-divisionally alternately disposed.

m−k MSBs of an average value of the duty ratio bit streams during the nframes may correspond to m−k MSBs of the first duty ratio bit stream.

According to an embodiment, a display device may include the followingelements: a pixel unit including a plurality of pixels; an emissioncontrol driver configured to supply an emission control signal fordetermining an emission period of the plurality of pixels; and a timingcontroller configured to determine a duty ratio of the emission controlsignal, using a duty ratio bit stream configured with m+k bits, whereinthe timing controller determines the duty ratio bit stream including kuppermost extension bits substituting for k LSBs, m−k MSBs, and the kLSBs having a fixed value, during n frames, wherein the k is a naturalnumber of 1 or more, and the n and m are natural numbers of 2 or more.

The n may be 2^(k).

Frames of a first group among the n frames may be emission-controlled tocorrespond to the duty ratio bit stream which is a first duty ratio bitstream, frames of a second group among the n frames may beemission-controlled to correspond to the duty ratio bit stream which isa second duty ratio bit stream, and the first duty ratio bit stream andthe second duty ratio bit stream are different.

The second duty ratio bit stream may have a value obtained by adding2^(k) to the first duty ratio bit stream.

The frames of the first group and the frames of the second group may betime-divisionally alternately disposed.

The other bits except k LSBs of an average value of the duty ratio bitstreams during the n frames may correspond to uppermost extension bitsand MSBs of the first duty ratio bit stream.

According to an embodiment, a method for driving/operating a displaydevice may include the following steps: supplying, by a timingcontroller, a control signal corresponding to a first duty ratio bitstream to an emission control driver; supplying, by the emission controldriver, an emission control signal having a duty ratio corresponding tothe first duty ratio bit stream to a pixel unit; supplying, by thetiming controller, a control signal corresponding to a second duty ratiobit stream to the emission control driver, wherein the second duty ratiobit stream has a value obtained by adding 2^(k) to a value of the firstduty ratio bit stream; and supplying, by the emission control driver, anemission control signal having a duty ratio corresponding to the secondduty bit stream to the pixel unit.

The sum of a number of frames of a first group, which areemission-controlled corresponding to the first duty ratio bit stream,and a number of frames of a second group, which are emission-controlledcorresponding to the second duty ratio bit stream, may be n. The k maybe a natural number of 1 or more, and the n may be a natural number of 2or more.

The n may be 2^(k).

The frames of the first group and the frames of the second group may betime-divisionally alternately disposed.

k LSBs of the first duty ratio bit stream may be 0, and k LSBs of thesecond duty ratio bit stream may be 0.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram (e.g., a block diagram) illustrating a displaydevice according to an embodiment.

FIG. 2 is a diagram (e.g., a block diagram) illustrating a timingcontroller according to an embodiment.

FIG. 3 is a diagram (e.g., a circuit diagram) illustrating a pixelaccording to an embodiment.

FIG. 4 is a timing diagram illustrating operation of the pixel of FIG. 3according to an embodiment.

FIG. 5 is a diagram (e.g., a block diagram) illustrating an emissioncontrol driver according to an embodiment.

FIG. 6 is a diagram (e.g., a circuit diagram) illustrating one stage ofthe emission control driver of FIG. 5 according to an embodiment.

FIG. 7 is a diagram illustrating a driving phase of a first driver ofthe stage of FIG. 6 according to an embodiment.

FIG. 8 is a diagram illustrating a driving phase of a third driver ofthe stage of FIG. 6 according to an embodiment.

FIG. 9 is a diagram illustrating a timing controller including theemission control driver of FIG. 5 according to an embodiment.

FIG. 10 is a diagram illustrating emission control according to anembodiment.

FIG. 11 is a diagram illustrating emission control according to anembodiment.

DETAILED DESCRIPTION

Example embodiments are described in detail with reference to theaccompanying drawings. Practical embodiments may be implemented invarious forms and are not limited to the example embodiments.

Although the terms “first,” “second,” etc. may be used herein todescribe various elements, these elements, should not be limited bythese terms. These terms may be used to distinguish one element fromanother element. Thus, a first element may be termed a second elementwithout departing from teachings of one or more embodiments. Thedescription of an element as a “first” element may not require or implythe presence of a second element or other elements. The terms “first,”“second,” etc. may also be used herein to differentiate differentcategories or sets of elements. For conciseness, the terms “first,”“second,” etc. may represent “first-type (or first-set),” “second-type(or second-set),” etc., respectively.

Same or similar constituent elements will be designated by samereference numerals.

The term “couple” may mean “electrically connected” or “electricallyconnected through no intervening transistor.”

FIG. 1 is a diagram illustrating a display device according to anembodiment.

Referring to FIG. 1, the display device 9 includes a timing controller10, a scan driver 20, an emission control driver 30, a data driver 40,and a pixel unit 50.

The timing controller 10 supplies a control signal CONT1 to the scandriver 10, supplies a control signal CONT3 to the emission controldriver 30, and supplies a control signal CONT2 and image signals R′, G′,and B′ to the data driver 40 by converting a control signal and imagesignals R, G, and B, which are supplied from the outside, to be suitablefor specifications of the display device 9. The control signal receivedby the timing controller 10 may include a horizontal synchronizationsignal Hsync and a vertical synchronization signal Vsync.

The scan driver 20 generates a scan signal to be supplied to a pluralityof scan lines S1, S2, . . . , and Sn by receiving the control signalCONT1. In an embodiment, the scan driver 20 may sequentially supply ascan signal to the plurality of scan lines S1, S2, . . . , and Sn. Forexample, the control signal CONT1 may include a gate start pulse GSP anda plurality of gate cock signals, and the scan driver 20 may beconfigured in the form of a shift register to generate a scan signal ina manner that sequentially transfer the gate start pulse to a next stagecircuit under the control of the gate clock signal.

The data driver 40 generates a data voltage to be supplied to aplurality of data lines D1, D2, . . . , and Dm by receiving the controlsignal CONT2 and the image signal R′, G′, and B′. Data voltagesgenerated in units of pixel rows may be simultaneously applied to theplurality of data lines D1, D2, . . . , and Dm according to an outputcontrol signal included in the control signal CONT2.

The pixel unit 50 may include a plurality of pixel circuits PX11, PX12,. . . , PX1m, PX21, PX22, . . . , PX2 m, . . . , PXn1, PXn2, . . . , andPXnm. Each pixel may have a substantially identical pixel circuitstructure. Each pixel circuit may be coupled to a corresponding dataline and a corresponding scan line, and receive a data voltage inputcorresponding to a scan signal. The emission control driver 30 maysupply emission control signals El, E2, . . . , and En for determiningemission periods of the plurality of pixel circuits PX11, PX12, . . . ,PX1m, PX21, PX22, . . . , PX2 m, . . . , PXn1, PXn2, . . . , and PXnm toemission control lines. For example, each pixel circuit may include anemission control transistor, and the flow of current through the organiclight emitting diode may be determined according to on/off of theemission control transistor, so that the emission of the organic lightemitting diode is controlled.

FIG. 2 is a diagram illustrating a timing controller according to anembodiment.

Referring to FIG. 2, the timing controller 10 may include a dimmingcontroller 110 and a signal converter 120.

The dimming controller 110 may determine a duty ratio of an emissioncontrol signal, using a duty ratio bit stream duty[7:0]. In thefollowing drawings from FIG. 2, for convenience of description, it isassumed that the duty ratio bit stream duty[7:0] has 8 bits. Inembodiments, the duty ratio bit stream may be configured with m bits tobe expressed as duty[(m−1):0]. Here, m may be a natural number of 2 ormore.

The dimming controller 110 may include a transistor coupled to each bitsignal line to express a binary level, i.e., 0 or 1 of each bit. Forexample, when the transistor is to be turned on, binary level 1 may beexpressed with a specific voltage applied to a corresponding bit signalline. When the transistor is to be turned off, binary level 0 may beexpressed with another voltage of the corresponding bit signal line. Theexisting open drain and open collector structures may be applied as thecoupling structure of the transistors and the bit signal lines. Apull-up resistor or a pull-down resistor may be coupled to thisstructure. Those skilled in the art may re-design various couplingrelations of the transistors and the bit signal lines of the dimmingcontroller 110.

In an embodiment, the dimming controller 110 may consume switchingcontrol power of all eight transistors to express the duty ratio bitstream duty[7:0].

According to an embodiment, k least significant bits (LSBs) in the dutyratio bit stream duty[7:0] may remain at a single/constant level/valueduring n frames. That the k LSBs are fixed as the single/constantlevel/value may mean that the k LSBs are maintained at the binary level0 for transistors of the dimming controller 110 that correspond to the kLSBs to be continuously off (i.e., remain off) during the n frames. Inan embodiment, k may be a natural number of 1 or more, and n may be anatural number of 2 or more. In an embodiment, n may be 2^(k).

For example, in the embodiment of FIG. 2, k may be 2 and n may be 4. Inan embodiment, b1 and b0 corresponding to the LSBs may be the binarylevel 0 during four frames.

That is, the timing controller 10 may determine a duty ratio bit streamincluding (m−k) most significant bits (MSBs) and k LSBs having a fixedvalue, during the n frames.

Accordingly, switching control is not separately performed ontransistors corresponding to LSBs, so that the power consumption of thedimming controller 110 can be reduced. Although the switching control isnot separately perform on the transistors corresponding to the LSBs,MSBs are partially changed, so that emission control can be performed toexpress a dimming level equal or approximate to a target dimming level.

The signal converter 120 converts the received duty ratio bit streamduty[7:0] to be suitable for specifications of the emission controldriver 30, and supplies the converted duty ratio bit stream as a portionof the control signal CONT3 to the emission control driver 30. Forexample, the signal converter 120 may be a serializer.

The emission control driver 30 may generate an emission control signalhaving a duty ratio corresponding to the duty ratio bit streamduty[7:0], based on the received control signal CONT3, and supply(instances/copies of) the generated emission control signals E1, E2, . .. , and En to the emission control lines.

In an embodiment, the timing controller 10 may determine a duty ratiobit stream including k uppermost extension bits substituting for the kLSBs, the (m−k) MSBs, and the k LSBs having a fixed value, for the nframes. In this embodiment, the duty ratio bit stream may be configuredto (m+k) bits.

For example, the timing controller 10 may express the k uppermostextension bits using bit signal lines corresponding to the k LSBs in theduty ratio bit stream duty[7:0], and the k LSBs may be assumed as 0during the n frames.

Referring to FIG. 2, the first MSB of the duty ratio bit streamduty[7:0] is b7, but LSBs b1 and b0 may be used as if they are b9 and b8as the uppermost extension bits. In an embodiment, the LSBs b1 and b0may be assumed as 0. In an embodiment, the eight transistors of thedimming controller 110 are all used, so that the number of expressibledimming levels can be increased without reducing switching controlpower. In particular, this is effective with respect to a low-resolutiondisplay panel.

In an embodiment, the k LSBs can be assumed as 0 for the n frames.

FIG. 3 is a diagram illustrating a pixel according to an embodiment.

FIG. 4 is a timing diagram illustrating the pixel of FIG. 3 according toan embodiment.

Referring to FIG. 3, the pixel PXij may include a plurality oftransistors T1, T2, and T3, a storage capacitor Cst, and an organiclight emitting diode OLED.

In an embodiment, the circuit of the pixel PXij is configured withP-type transistors. In an embodiment, the circuit may include N-typetransistors.

One end of the transistor T2 may be coupled to a data line Dj, and agate terminal of the transistor T2 may be coupled to a scan line Si. Thetransistor T2 may be called as a scanning transistor.

A gate terminal of the transistor T1 may be coupled to the other end ofthe transistor T2, and one end of the transistor T1 may be coupled to avoltage source ELVDD. The transistor T1 may be called as a drivingtransistor.

The storage capacitor Cst may connect the gate terminal and one end ofthe transistor T1.

One end of the transistor T3 may be coupled to the other end of thetransistor T1, a gate terminal of the transistor T3 may be coupled to anemission control line Ei, and the other end of the transistor T3 may becoupled to an anode of the organic light emitting diode OLED. Thetransistor T3 may be called as an emission control transistor.

A cathode of the organic light emitting diode OLED may be coupled to avoltage source ELVSS.

Referring to FIG. 4, when a scan signal having a low level is suppliedthrough the scan line Si, the transistor T2 is turned on, and a datavoltage DATA applied to the data line Dj is applied to the gate terminalof the transistor T1 through the turned-on transistor T2.

The storage capacitor Cst stores a voltage corresponding to thedifference between the data voltage DATA and the voltage source ELVSS.Since the transistor T3 is in an off-state, no current flows through theorganic light emitting diode OLED even when the transistor T1 is turnedon.

When an emission control signal having a low level is supplied throughthe emission control line Ei, a driving current flows toward the organiclight emitting diode OLED from the voltage source ELVDD through thetransistor T1 and the transistor T3. Thus, the organic light emittingdiode OLED emits light with a luminance that is in proportion to themagnitude of the driving current. In an embodiment, the magnitude of thedriving current is in proportion to a voltage maintained by the storagecapacitor Cst.

The duty ratio of the emission control signal may be a ratio of a time(or duration) for which the emission control signal having the low levelflows through the emission control line Ei to a time (or duration) forwhich the emission control signal having a high level flows through theemission control line Ei. For example, as the duty ratio of the emissioncontrol signal becomes higher, the time for which the emission controlsignal having the low level flows to allow the emission controltransistor T3 to be turned on may become longer. As the duty ratio ofthe emission control signal becomes lower, the time for which theemission control signal having the high level flows to allow theemission control transistor T3 to be/remain turned off may becomelonger.

In an embodiment, the duty ratio of the emission control signal may beassociated with a frame.

FIG. 5 is a diagram illustrating an emission control driver according toan embodiment.

Referring to FIG. 5, the emission control driver 30′ receives, as thecontrol signal CONT3, a plurality of clock signals CLK1, CLK2, and CLK3and two start signals SP1 and SP2, and includes a plurality of stages321, 322, 323, 324, 325.

The plurality of stages 321, 322, 323, 324, 325, . . . may be coupled toemission control lines El, E2, E3, E4, E5, . . . , respectively.

Each of the stages 322, 323, 324, 325, . . . as start signals, outputsignals OS1 and OS2 output from a previous stage thereof.

In an embodiment, the clock signal CLK2 is supplied to all of the stages321, 322, 323, 324, 325, . . . , the clock signal CLK1 is supplied toodd-numbered stages 321, 323, 325, . . . , and the clock signal CLK3 issupplied to even-numbered stages 322, 324.

The clock signals CLK1, CLK2, and CLK3 may be set to have the sameperiod, and a first start signal SP1 and a second start signal SP2 maybe supplied once or more times during one frame period.

According to an embodiment, the width of an emission control signal maybe determined corresponding to a width (or interval/space) between thefirst start signal SP1 and the second start signal SP2 (i.e., a timeuntil the second start signal SP2 has the low level after the firststart signal SP1 has the low level). For example, as the width betweenthe first start signal SP1 and the second start signal SP2 is set wider,the duty ratio of the emission control signal may become lower. Forexample, as the width between the first start signal SP1 and the secondstart signal SP2 is set narrower, the duty ratio of the emission controlsignal may become higher.

The width between a first output signal OS1 and a second output signal0S2 output from the first stage 321 may correspond to that between thefirst start signal SP1 and the second start signal SP2. Therefore, theother stages 322, 323, 324, 325, . . . may all have the same duty ratioof the emission control signal as that associated with the first stage321.

FIG. 6 is a diagram illustrating one stage of the emission controldriver of FIG. 5 according to an embodiment. FIG. 7 is a diagramillustrating a driving/operating phase of a first driver of the stage ofFIG. 6 according to an embodiment. FIG. 8 is a diagram illustrating adriving/operating phase of a third driver of the stage of FIG. 6according to an embodiment.

Referring to FIG. 6, a circuit of the first stage 321 of the emissioncontrol driver 30′ is illustrated. Circuit configurations of the otherstages 322, 323, 324, 325, . . . may be substantially identical to thatof the first stage 321 except connections related to input signals, andtherefore the first stage 321 is described as an example for all thesestages.

The first stage 321 may include a first driver 3211, a second driver3212, and a third driver 3213.

The first driver 3211 may generate a first output signal OS1 using clocksignals CLK1 and CLK2 and a first start signal SP1.

The second driver 1312 may generate a second output signal OS2 usingclock signals CLK1 and CLK2 and a second start signal SP2. The circuitconfiguration of the second driver 3212 may be identical to that of thefirst driver 3211.

The third driver 3213 may generate an emission control signal E1 usingthe first output signal OS1 and the second output signal OS2.

The first driver 3211 outputs the voltage of a voltage source VDD or theclock signal CLK1 as the first output signal OS1. In an embodiment, thefirst driver 3211 includes six transistors M11 to M16 and two capacitorsC11 and C12.

The voltage source VDD is set to a voltage higher than that of a voltagesource VSS. For example, the voltage source VDD may be set to a voltageat which the transistors can be turned off, and the voltage source VSSmay be set to a voltage at which the transistors can be turned on.

One end of the transistor M15 is coupled to the voltage source VDD, andthe other end of the transistor M15 is coupled to an output terminalout1. In addition, a gate terminal of the transistor M15 is coupled to anode N11.

On end of the transistor M16 is coupled to the output terminal out1, andthe other end of the transistor M16 is coupled to an input terminal 36.In addition, a gate terminal of the transistor M16 is coupled to a nodeN12. The input terminal 36 is supplied with the clock signal CLK1.

One end of the transistor M14 is coupled to the node N11, and the otherend of the transistor M14 is coupled to the voltage source VSS. Inaddition, a gate terminal of the transistor M14 is coupled to an inputterminal 35. The input terminal 35 is supplied with the clock signalCLK2.

One end of the transistor M13 is coupled to the voltage source VDD, andthe other end of the transistor M13 is coupled to the node N12. Inaddition, a gate terminal of the transistor M13 is coupled to the nodeN11.

One end of the transistor M12 is coupled to the voltage source VDD, andthe other end of the transistor M12 is coupled to the node N11. Inaddition, a gate terminal of the transistor M12 is coupled to an inputterminal 33. The input terminal 33 is supplied with the first startsignal SP1.

One end of the transistor M11 is coupled to the node N12, and the otherend of the transistor M11 is coupled to the voltage source VSS. Inaddition, a gate terminal of the transistor M11 is coupled to the inputterminal 33.

The capacitor C11 is coupled between the gate terminal of the transistorM15 and the voltage source VDD. The capacitor C11 charges a voltagecorresponding to the turn-on or turn-off of the transistor M15.

The capacitor C12 is coupled between the gate terminal of the transistorM16 and the output terminal out1. The capacitor C12 charges a voltagecorresponding to the turn-on or turn-off of the transistor M16.

In an embodiment, the configuration of the second driver 3212 isidentical to that of the first driver 3211 except that the second startsignal SP2 is supplied to an input terminal 33′. Therefore, descriptionscommon to the first driver 3211 and the second driver 3212 are notrepeated.

FIG. 7 is a diagram illustrating an operation process of the firstdriver 3211 according to an embodiment.

The operation process is described with reference to FIGS. 6 and 7. Whenthe first start signal SP1 is supplied at a low level, the transistorM11 and the transistor M12 are turned on.

When the transistor M11 is turned on, the voltage of the voltage sourceVSS is supplied to the node N12. When the voltage of the voltage sourceVSS is supplied to the node N12, the transistor M16 is turned on. Whenthe transistor M16 is turned on, the input terminal 36 is coupled to theoutput terminal out1. In addition, a voltage corresponding to theturn-on of the transistor M16 is charged in the capacitor C12.

In an embodiment, When the transistor M12 is turned on, the voltage ofthe voltage source VDD is supplied to the node N11. When the voltage ofthe voltage source VDD is supplied to the node N11, the transistor M13and the transistor M15 are turned off.

Subsequently, the first start signal SP1 is supplied at a high level.When the first start signal SP1 is supplied at the high level, thetransistor M11 and the transistor M12 are turned off. At this time, thetransistor M16 maintains the turn-on state due to the voltage charged inthe capacitor C12. The clock signal CLK1 is supplied to the outputterminal out1 during a period in which the transistor M16 maintains theturn-on state.

After the clock signal CLK1 is supplied, the clock signal CLK2 issupplied. When the clock signal CLK2 is supplied, the transistor M14 isturned on. When the transistor M14 is turned on, the voltage of thevoltage source VSS is supplied to the node N11. When the voltage of thevoltage source VSS is supplied to the node N11, the transistor M13 andthe transistor M15 are turned on.

When the transistor M13 is turned on, the voltage source VDD is coupledto the node N12. Accordingly, the transistor M16 is turned off. When thetransistor M15 is turned on, the voltage source VDD is coupled to theoutput terminal out1. At this time, the capacitor C11 charges a voltagecorresponding to the turn-on of the transistor M15. In an embodiment,the transistor M15 supplies the voltage of the voltage source VDD to theoutput terminal out1 until before the transistor M12 is turned on by anext first start signal SP1.

As described above, the first driver 3211 supplies a next clock signalCLK1 (low level) to the output terminal out1 after the first startsignal SP1 is supplied. Similarly, the second driver 3212 supplies anext clock signal CLK1 to an output terminal out2 when the second startsignal SP2 is supplied. Thus, the interval between the first outputsignal OS1 and the second output signal OS2, which are respectivelyoutput from the first driver 1311 and the second driver 1312,corresponds to that between the first start signal SP1 and the secondstart signal SP2.

The configuration of the third driver 3213 is described with referenceto FIG. 6.

In the third driver 3213, the voltage source VDD or the voltage sourceVSS is coupled to an output terminal out3, corresponding to the firstoutput signal OS1 and the second output signal OS2. In an embodiment,the third driver 3213 includes six transistors M1 to M6 and twocapacitors C1 and C2.

One end of the transistor M1 is coupled to the voltage source VDD, andthe other end of the transistor M1 is coupled to the output terminalout3. In addition, a gate terminal of the transistor M1 is coupled to anode N1.

One end of the transistor M2 is coupled to the output terminal out3, andthe other end of the transistor M2 is coupled to the voltage source VSS.In addition, a gate terminal of the transistor M2 is coupled to a nodeN2.

One end of the transistor M3 is coupled to the voltage source VDD, andthe other end of the transistor M3 is coupled to the node N1. Inaddition, a gate terminal of the transistor M3 is coupled to the nodeN2.

The capacitor C1 is coupled between the gate terminal of the transistorM2 and the output terminal out3. The capacitor C1 stores a voltagecorresponding to the turn-on or turn-off of the transistor M2.

The capacitor C2 is coupled between the gate terminal of the transistorM1 and the voltage source VDD. The capacitor C2 charges a voltagecorresponding to the turn-on or turn-off of the transistor M1.

One end of the transistor M5 is coupled to the voltage source VDD, andthe other end of the transistor M5 is coupled to the node N2. Inaddition, a gate terminal of the transistor M5 is coupled to an inputterminal 37. The input terminal 37 is supplied with the first outputsignal OS1.

One end of the transistor M6 is coupled to the node N2, and the otherend of the transistor M6 is coupled to the voltage source VSS. Inaddition, a gate terminal of the transistor M6 is coupled to an inputterminal 38. The input terminal 38 is supplied with the second outputsignal OS2.

One end of the transistor M4 is coupled to the node N1, and the otherend of the transistor M4 is coupled to the voltage source VSS. Inaddition, a gate terminal of the transistor M4 is coupled to the inputterminal 37. The fourth transistor M4 is turned on or turned offcorresponding to a voltage supplied to the input terminal 37.

FIG. 8 is a diagram illustrating an operation process of the thirddriver 3213 according to an embodiment.

When the first output signal having a low level is supplied to the inputterminal 37, the transistor M4 and the transistor M5 are turned on. Atthis time, since the input terminal 38 is supplied with a high-levelvoltage, the transistor M6 is turned off.

When the transistor M5 is turned on, the voltage of the voltage sourceVDD is supplied to the node N2. In an embodiment, the transistor M2 andthe transistor M3, which are coupled to the node N2, are turned off.

When the transistor M4 is turned on, the voltage of the voltage sourceVSS is supplied to the first node N1. In an embodiment, the transistorM1 coupled to the node N1 is turned on. When the transistor M1 is turnedon, the voltage of the voltage source VDD is supplied to the outputterminal out3. Thus, an emission control signal having a high level issupplied to an emission control line E1 coupled to the output terminalout3.

In an embodiment, the capacitor C2 charges a voltage corresponding tothe turn-on of the transistor M1, and the capacitor C1 charges a voltagecorresponding to the turn-off of the transistor M2. Thus, as ahigh-level voltage is supplied to the input terminal 37, the voltage ofthe voltage source VDD is supplied to the output terminal out3 while thetransistor M1 is maintaining the turn-on state and the transistor M2 ismaintaining the turn-off state even when the transistors M4 and M5 areturned off.

Subsequently, as the second output signal OS2 having the low level issupplied to the input terminal 38, the transistor M6 is turned on. Atthis time, as the high-level voltage is supplied to the input terminal37, the transistor M4 and the transistor M5 are in the turn-off state.

When the transistor M6 is turned on, the voltage of the voltage sourceVSS is supplied to the node N2. In an embodiment, the transistor M3 andthe transistor M2, which are coupled to the node N2, are turned on.

When the transistor M3 is turned on, the voltage of the voltage sourceVDD is supplied to the node N1. In an embodiment, the transistor M1coupled to the node N1 is turned off. When the transistor M2 is turnedon, the voltage of the voltage source VSS is supplied to the outputterminal out3. Thus, the emission control signal having the low level issupplied to the emission control line E1 coupled to the output terminalout3.

FIG. 9 is a diagram illustrating a timing controller including theemission control driver discussed with reference to FIG. 5 according toan embodiment.

Referring to FIG. 9, like FIG. 2, the timing controller 10 includes adimming controller 110 and a signal converter 120′. The signal converter120′ is configured suitable for the configuration of the emissioncontrol driver 30′.

The signal converter 120′ may supply the second start signal SP2 havingthe low level such that the duty ratio of the emission control signalcorrespond to the duty ratio bit stream duty[7:0]. As described above,the duty ratio of the emission control signal may be controlled bycontrolling the interval between the first start signal SP1 having thelow level and the second start signal having the low level.

The control of the duty ratio bit stream duty[7:0], which is performedby the dimming controller 110, may have features substantially identicalto or analogs to features discussed with reference to FIG. 2, andtherefore related descriptions are not repeated.

FIG. 10 is a diagram illustrating emission control according to anembodiment.

Referring to FIG. 10, frames may be separated based on the verticalsynchronization signal Vsync. The emission control driver 30 may beimplemented in the form of a shift register, and emission controlsignals E2, E3, . . . having a pulse form substantially identical tothat of the emission control signal E1 from the first stage may besequentially output from next stages. The emission control driver 30′described with reference to FIGS. 5 to 8 may be an example of theemission control driver 30.

Referring to FIG. 10, the timing controller 10 determines a duty ratiousing all of the LSBs and MSBs of the duty ratio bit stream duty[7:0].In FIG. 10, the LSB set is represented by 2′b10 (i.e., b1=1 and b0=0).

Since information on all bits of the duty ratio bit stream duty[7:0] isrequired, it is required to drive of all transistors coupled to therespective bit signal lines of the dimming controller 110, and theswitching power of the dimming controller 110 is not reduced.

FIG. 11 is a diagram illustrating emission control according to anembodiment.

In an embodiment, k is 2, and n is 4.

Referring to FIG. 11, the timing controller 10 determines a duty ratiousing (m−k) MSBs without using k LSBs in the duty ratio bit streamduty[7:0]. That is, the timing controller 10 determines a duty ratiousing six MSBs but not two LSBs.

The dimming controller 110 does not control the switching of transistorscoupled to bit signal lines corresponding to the two LSBs. In anembodiment, a default voltage corresponding to the binary level 0 may beapplied to the bit signal lines corresponding to the LSBs. Thus, theswitching control power consumption of transistors corresponding to theLSBs in the timing controller 10 can be reduced.

Since the timing controller 10 does not use the LSBs, a duty ratioequivalent/equal to that in FIG. 10 is to be expressed using only theMSBs. In an embodiment, the MSBs can express a duty ratio equal orapproximate to that of FIG. 10 using a first duty ratio bit streamduty1[7:0] and a second duty ratio bit stream duty2[7:0], which aredifferent from each other.

Frames of a first group among the n frames may be emission-controlledaccording to the first duty ratio bit stream duty1[7:0], and frames of asecond group among the n frames may be emission-controlled according tothe second duty ratio bit stream duty2[7:0].

In order to reduce switching power consumption, LSBs of the first dutyratio bit stream duty1[7:0] and the second duty ratio bit streamduty2[7:0] are not used, and therefore, each LSB may be set as 0.

If the total emission time and the total non-emission time associatedwith FIG. 11 are equal or approximate to the total emission time and thetotal non-emission time associated with FIG. 10 for n frames, an overallduty ratio equal or approximate to that of FIG. 10 may be expressed inthe configuration associated with FIG. 11. That is, when the total sumof a time (C*2) for which the emission control transistor is turned offby the first duty ratio bit stream duty1[7:0] and a time (B*2) for whichthe emission control transistor is turned off by the second duty ratiobit stream duty2[7:0] for the four frames illustrated in FIG. 11 isequal to a time (A*4) for which the emission control transistor isturned off by the duty ratio bit stream duty[7:0] for the four framesillustrated in FIG. 10, the same dimming level may be expressed. Thatis, (m−k) MSBs of an average value of the duty ratio bit streams duringthe n frames may correspond to (m−k) MSBs of the first duty ratio bitstream, and a dimming level equal or approximate to that of FIG. 10.

In an embodiment, the second duty ratio bit stream duty2[7:0] may have avalue obtained by adding 2^(k) to a value of the first duty ratio bitstream duty1[7:0]. Since the duty ratio bit stream has k LSBs, the valueof the LSBs is not changed even though 2^(k) (decimal number expression)is added. In the configuration associated with FIG. 11, since k is 2,the second duty ratio bit stream duty2[7:0] has a value obtained byadding 4 (decimal number expression) to the first duty ratio bit streamdutyl[7:0].

In an embodiment, the second duty ratio bit stream duty2[7:0] may have avalue obtained by adding a value larger than 2^(k) to the first dutyratio bit stream duty1[7:0].

In an embodiment, the frames of the first group and the frames of thesecond group may be time-divisionally alternately disposed/arranged.Accordingly, dithering is implemented, and thus it is possible toprovide an image that is smoothly viewed by a user sensitive to a changein brightness.

In an embodiment, the LSB set is 2′b10 (i.e., b1=1 and b0=0), and twosecond duty ratio bit streams duty2[7:0] and two first duty ratio bitstreams duty1[7:0] may be provided for four frames.

In an embodiment, the LSB set is 2′b11 (i.e., b1=1 and b0=1), and threesecond duty ratio bit streams duty2[7:0] and one first duty ratio bitstream dutyl[7:0] may be provided for four frames.

In an embodiment, the LSB set is 2′b01 (i.e., b1=0 and b0=1), and onesecond duty ratio bit stream duty2[7:0] and three first duty ratio bitstreams duty1[7:0] may be provided for four frames.

In an embodiment, the LSB set is 2′b00 (i.e., b1=0 and b0=0), no secondduty ratio bit stream duty2[7:0] and four first duty ratio bit streamsduty1[7:0] may be provided for four frames, and duty ratio bit streamsassociated with the configuration of FIG. 10 may be equivalent to dutyratio bit streams associated with the configuration of FIG. 11.

The parameter values k=2, n=4, and m=8 are given as examples. Theparameter values may be configured according to particular embodiments,e.g., particular products and/or operating environments.

In a display device and a driving method thereof according to anembodiment, a dimming level similar to a target dimming level can beexpressed with minimum switching power consumption of the dimmingcontroller.

In a display device and a driving/operating method thereof according toan embodiment, the number of dimming levels expressible in alow-resolution display panel can be maximized.

Example embodiments have been described. Although specific terms areemployed, they are to be interpreted in a generic and descriptive senseand not for purpose of limitation. In some instances, features,characteristics, and/or elements described in connection with aparticular embodiment may be used singly or in combination withfeatures, characteristics, and/or elements described in connection withother embodiments unless otherwise specifically indicated. Variouschanges in form and details may be made to the described embodimentswithout departing from the spirit and scope set forth in the followingclaims.

What is claimed is:
 1. A display device comprising: a pixel; an emissioncontrol driver configured to supply an emission control signal fordetermining emission periods and non-emission periods of the pixel; anda timing controller configured to determine a duty ratio of the emissioncontrol signal, based on a duty ratio bit stream configured with aplurality of bits, wherein the timing controller determines the dutyratio, by using partial bits among the plurality of bits of the dutyratio bit stream, and wherein a first length of one of the emissionperiods for a first frame is different from a second length of one ofthe emission periods for a second frame.
 2. The display device of claim1, wherein the plurality of bits of the duty ratio bit stream are mbits, wherein the partial bits are m−k most significant bits (MSBs) ofthe duty ratio bit stream, and wherein the k is a natural number of 1 ormore, and the m is a natural number of 2 or more.
 3. The display deviceof claim 1, wherein the first length is determined by a first duty ratiobit stream, and wherein the second length is determined by a second dutyratio bit stream.
 4. The display device of claim 3, wherein the secondduty ratio bit stream has a value obtained by adding 2^(k) to the firstduty ratio bit stream, and wherein the k is a natural number of 1 ormore.
 5. The display device of claim 4, wherein the first frame and thesecond frame are time-divisionally alternately disposed.
 6. The displaydevice of claim 2, wherein m−k MSBs of an average value of duty ratiobit streams during consecutive frames correspond to m−k MSBs of a firstduty ratio bit stream determining the first length.
 7. A method fordriving a display device, the method comprising: determining, by atiming controller, a first duty ratio of an emission control signal byusing partial bits among a plurality bits of a first duty ratio bitstream, the emission control signal determining emission periods andnon-emission periods of a pixel; supplying, by the timing controller, acontrol signal corresponding to the first duty ratio to an emissioncontrol driver; supplying, by the emission control driver, the emissioncontrol signal corresponding to the first duty ratio to the pixel, for afirst frame; determining, by the timing controller, a second duty ratioof the emission control signal by using partial bits among a pluralitybits of a second duty ratio bit stream; supplying, by the timingcontroller, a control signal corresponding to the second duty ratio tothe emission control driver; and supplying, by the emission controldriver, the emission control signal corresponding to the second dutyratio to the pixel, for a second frame, wherein a first length of one ofthe emission periods for the first frame is different from a secondlength of one of the emission periods for the second frame.
 8. Themethod of claim 7, wherein the plurality of bits of each of the firstand second duty ratio bit streams are m bits, wherein the partial bitsof each of the first and second duty ratio bit streams are m−k mostsignificant bits (MSBs), and wherein the k is a natural number of 1 ormore, and the m is a natural number of 2 or more.
 9. The method of claim7, wherein the first frame and the second frame are time-divisionallyalternately disposed.
 10. The method of claim 8, wherein m−k MSBs of anaverage value of duty ratio bit streams during consecutive framescorrespond to m−k MSBs of the first duty ratio bit stream determiningthe first length.